Organic light emitting diode display and fabricating method thereof

ABSTRACT

An organic light emitting diode display and a fabrication method thereof, the display including a substrate; a thin film transistor on the substrate; and an organic light emitting diode on the substrate, the organic light emitting diode including a pixel electrode, an organic emission layer, and a common electrode, wherein the organic emission layer includes a red (R) pixel, a green (G) pixel, and a blue (B) pixel, the pixel electrode includes a first pixel electrode, a second pixel electrode, and a third pixel electrode that respectively correspond to the red pixel, the green pixel, and the blue pixel, the first pixel electrode, the second pixel electrode, and the third pixel electrode each have different thicknesses, and the first pixel electrode, the second pixel electrode, and the third pixel electrode each include a first hydrophobic layer.

BACKGROUND

1. Field

Embodiments relate to an organic light emitting diode display and afabricating method thereof.

2. Description of the Related Art

An organic light emitting diode (OLED) display is a flat panel displaythat may be lightweight and thin, may exhibit a self-luminouscharacteristic, and may not require a separate light source. The OLEDdisplay may exhibit quality characteristics, e.g., low powerconsumption, high luminance, and high response speed, and as such, theOLED display is receiving much attention as a next-generation displaydevice.

An organic light emitting diode display may include an organic lightemitting diode including an anode, an organic emission layer, and acathode. Holes and electrons may be injected from the anode and thecathode, respectively, to form excitons. The excitons may transition toa ground state, thereby causing the organic light emitting diode to emitlight.

A lifespan of such an organic light emitting diode may be limited. Forexample, the lifespan of the organic light emitting diode may beaffected by degradation of organic materials, interfacialcharacteristics of organic materials, and so on. A method for improvinginterfacial characteristics by forming a buffer layer under each pixelin order to improve the lifespan of an organic light emitting diode hasbeen proposed.

For example, the organic light emitting diode may include a red pixel(R), a green pixel (G), and a blue pixel (B); and the lifespan variesfrom pixel to pixel. To compensate for differences in lifespan amongpixels, each pixel may include a buffer layer formed thereunder. Forexample, thickness of the respective buffer layers may differ from pixelto pixel.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY

Embodiments are directed to an organic light emitting diode display anda fabricating method thereof.

At least one of the above and other features and advantages may berealized by providing an organic light emitting diode display includinga substrate; a thin film transistor on the substrate; and an organiclight emitting diode on the substrate, the organic light emitting diodeincluding a pixel electrode, an organic emission layer, and a commonelectrode, wherein the organic emission layer includes a red (R) pixel,a green (G) pixel, and a blue (B) pixel, the pixel electrode includes afirst pixel electrode, a second pixel electrode, and a third pixelelectrode that respectively correspond to the red pixel, the greenpixel, and the blue pixel, the first pixel electrode, the second pixelelectrode, and the third pixel electrode each have differentthicknesses, and the first pixel electrode, the second pixel electrode,and the third pixel electrode each include a first hydrophobic layer.

A thickness of the first pixel electrode may be greater than a thicknessof the second pixel electrode, and a thickness of the second pixelelectrode may be greater than a thickness of the third pixel electrode.

The first pixel electrode may include a sequentially stacked first ITO(indium tin oxide) layer, Ag (silver) layer, second ITO layer, third ITOlayer, and fourth ITO layer, the first hydrophobic layer may be betweenthe second ITO layer and the third ITO layer, and the first pixelelectrode may further include a second hydrophobic layer, the secondhydrophobic layer being between the third ITO layer and the fourth ITOlayer.

The first ITO layer, the second ITO layer, and the third ITO layer mayeach include polycrystalline ITO.

The second pixel electrode may include a sequentially stacked first ITOlayer, Ag layer, second ITO layer, and third ITO layer, and the firsthydrophobic layer may be between the second ITO layer and the third ITOlayer.

The second pixel electrode may further include a second hydrophobiclayer, the second hydrophobic layer being on the third ITO layer.

The first ITO layer, the second ITO layer, and the third ITO layer mayeach include polycrystalline ITO.

The third pixel electrode may include a sequentially stacked first ITOlayer, Ag layer, and second ITO layer, and the first hydrophobic layermay be on the second ITO layer.

The first ITO layer and the second ITO layer may each includepolycrystalline ITO.

The first hydrophobic layer may have a thickness of about 30 Å to about50 Å.

The organic emission layer may further include at least one of a holeinjection layer, a hole transporting layer, an electron transportinglayer, and an electron injection layer.

The organic light emitting diode display may further include areflective layer on the common electrode.

At least one of the above and other features and advantages may also berealized by providing a fabricating method of an organic light emittingdiode display, the method including providing a substrate; forming athin film transistor on the substrate; forming a pixel electrode on thethin film transistor; forming an organic emission layer on the pixelelectrode; and forming a common electrode on the organic emission layer,wherein the pixel electrode includes a first hydrophobic layer and asecond hydrophobic layer, and thicknesses of portions of the pixelelectrode corresponding to a red pixel, a green pixel, and a blue pixelof the organic emission layer, respectively, are different from eachother.

Forming the pixel electrode may include forming a first pixel electrode,a second pixel electrode, and a third pixel electrode under each of andcorresponding to the red pixel, the green pixel, and the blue pixel,respectively, a thickness of the first pixel electrode may be greaterthan a thickness of the second pixel electrode, and a thickness of thesecond pixel electrode may be greater than a thickness of the thirdpixel electrode.

Forming the pixel electrode may include sequentially stacking a firstITO layer, a Ag layer, and a second ITO layer; forming the firsthydrophobic layer on the second ITO layer; forming a third ITO layer onthe first hydrophobic layer; removing a part of the third ITO layer;forming the second hydrophobic layer on the third ITO layer; forming afourth ITO layer on the second hydrophobic layer; and removing a part ofthe fourth ITO layer.

Forming the pixel electrode may further include polycrystallizing thefirst ITO layer and the second ITO layer prior to forming the firsthydrophobic layer.

Polycrystallizing the first ITO layer and the second ITO layer mayinclude a heat treatment.

Removing the part of the third ITO layer may include forming aphotoresist layer on portions of the third ITO layer corresponding tothe red pixel and the green pixel; etching portions of the third ITOlayer corresponding to the blue pixel; and removing the photoresistlayer.

Forming the pixel electrode may further include polycrystallizing thethird ITO layer prior to forming the second hydrophobic layer.

Polycrystallizing the third ITO layer may include a heat treatment.

Removing the part of the fourth ITO layer may include forming aphotoresist layer on a portion of the fourth ITO layer corresponding tothe red pixel; etching portions of the fourth ITO layer corresponding tothe green pixel and the blue pixel; and removing the photoresist layer.

The first hydrophobic layer and the second hydrophobic layer may eachhave a thickness of about 30 Å to about 50 Å.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages will become more apparent tothose of ordinary skill in the art by describing in detail exemplaryembodiments with reference to the attached drawings, in which:

FIG. 1 illustrates a block diagram schematically showing an organiclight emitting diode display according to an embodiment;

FIG. 2 illustrates a cross-sectional view showing an internalconfiguration of the organic light emitting diode display of FIG. 1;

FIG. 3 illustrates an enlarged cross-sectional view of a pixel electrodeof the organic light emitting diode display of FIG. 2; and

FIGS. 4A to 4G illustrate stages in a fabricating process of a pixelelectrode of an organic light emitting diode display according to anembodiment.

DETAILED DESCRIPTION

Korean Patent Application No. 10-2010-0063962, filed on Jul. 2, 2010, inthe Korean Intellectual Property Office, and entitled: “Organic LightEmitting Diode Display And Fabricating Method Thereof,” is incorporatedby reference herein in its entirety.

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

In the drawing figures, the dimensions of layers and regions may beexaggerated for clarity of illustration. It will also be understood thatwhen a layer or element is referred to as being “on” another layer orsubstrate, it can be directly on the other layer or substrate, orintervening layers may also be present. Further, it will be understoodthat when a layer is referred to as being “under” another layer, it canbe directly under, and one or more intervening layers may also bepresent. In addition, it will also be understood that when a layer isreferred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent. Like reference numerals refer to like elements throughout.

FIG. 1 illustrates a block diagram schematically showing an organiclight emitting diode display according to an embodiment. FIG. 2illustrates a cross-sectional view showing an internal configuration ofthe organic light emitting diode display of FIG. 1.

Referring to FIG. 1, the organic light emitting diode according to thepresent embodiment may include a plurality of gate lines 31, a pluralityof data lines 21 intersecting the plurality of gate lines 31 andinsulated therefrom, and a common voltage line 23 formed parallel to thedata lines 21, on a display substrate 100. The gate lines 31 and thedata lines 21 may respectively generate a gate voltage and a datavoltage, and may be connected to a gate driver 30 and a data driver 20that provide these voltages. The common voltage line 23 may also beconnected to the data driver 20.

A plurality of pixels may be formed in a matrix at areas where theplurality of gate lines 31 and the plurality of data lines 21 intersecteach other. Each pixel may include a switching thin film transistor 40,a driving thin film transistor 50, a capacitor 60, and an organic lightemitting diode 200.

The switching thin film transistor 40 may be used as a switching elementto select a pixel to emit light, with a switching gate electrode beingconnected to the gate lines 31 and a switching source electrode and aswitching drain electrode being respectively connected to the data lines31 and the capacitor 60. The driving thin film transistor 50 may causethe organic light emitting diode 200 within the selected pixel to emitlight. A driving gate electrode may be connected to the capacitor 60, adriving source electrode may be connected to the common voltage line 23,and a driving drain electrode may be connected to the organic lightemitting diode 200.

A voltage corresponding to a voltage difference between a common voltageapplied to the driving thin film transistor 50 from the common voltageline 23 and the data voltage transmitted from the switching thin filmtransistor 40 may be stored in the capacitor 60. A current correspondingto the voltage stored in the capacitor 60 may flow to the organic lightemitting diode 200 through the driving thin film transistor 50 so thatthe organic light emitting diode 200 emits light. The structure of theorganic light emitting diode display is merely illustrative, and theembodiments are not limited thereto. Those skilled in the art willappreciate that various modifications of the structure for driving theorganic light emitting diode can be made.

Referring to FIG. 2, the organic light emitting diode display accordingto the present embodiment may include the organic light emitting diode200 stacked on the display substrate 100 where the switching thin filmtransistor 40, the driving thin film transistor 50, and the capacitor 60are formed. Moreover, an encapsulator (not illustrated), e.g., anencapsulation substrate or thin film encapsulation layer, for sealingthe organic light emitting diode 200 may be further formed on theorganic light emitting diode 200.

The organic light emitting diode 200 may include a pixel electrode 240,an organic emission layer 201 on the pixel electrode, and a commonelectrode 280 on the organic emission layer 201. Depending upon adriving method of the organic light emitting diode display, the pixelelectrode 240 may be an anode and the common electrode 280 may be acathode, or vice versa. Although the present embodiment has beendescribed with respect to a case where the pixel electrode 240 is ananode and the common electrode 280 is a cathode, the embodiments are notlimited thereto.

The pixel electrode 240 may be connected to the driving thin filmtransistor 50 on the display substrate 100, whereby a voltage forcausing the organic emission layer 201 of the organic light emittingdiode 200 to emit light may be applied. Each pixel electrode 240 maycorrespond to each of RGB pixels 260R, 260G, and 260B to be describedbelow. In addition, adjacent pixel electrodes 240 may be spaced apartfrom each other.

The organic emission layer 201 including, e.g., a low-molecular weightorganic material or a high-molecular weight organic material may beformed on the pixel electrode 240. The organic emission layer 201 mayinclude an emission layer 260 including a red pixel 260R, a green pixel260G, and a blue pixel 260B. The RGB pixels 260R, 260G, and 260B may beformed in such a manner that, as illustrated in FIG. 2, adjacent pixelsare continuously formed, or in such a manner that, like the pixelelectrode 240, adjacent pixels are spaced apart from each other.

The organic emission layer 201 may further include at least one of ahole injection layer (HIL) 251, a hole transporting layer (HTL) 253, anelectron transporting layer (ETL) 271, and an electron injection layer(EIL) 273 in addition to the emission layer 260. If the organic emissionlayer 201 includes all of the layers, as shown in FIG. 2, the holeinjection layer 251 and the hole transporting layer 253 may be formedbetween the pixel electrode 240 and the emission layer 260; and theelectron transporting layer 271 and the electron injection layer 273 maybe formed on the emission layer 260 and the common electrode 280.

The common electrode 280 may be formed on the organic emission layer 201and may cover an entire area of, e.g., the substrate 100, unlike thepixel electrode 240. The common electrode may be formed of, e.g., Al(aluminum), Ag (silver), or a MgAg (magnesium-silver) alloy, and mayexhibit excellent conductivity and a high reflection characteristic. Inthe present embodiment, the organic light emitting diode display mayhave a bottom emission structure for emitting light in a direction ofthe display substrate 100. Thus, a reflective layer 290 for reflectinglight toward the display substrate 100 may be further included on thecommon electrode 280. The reflective layer 290 may include a metal,e.g., Al, Ag, or the like, having excellent reflectivity. However, theembodiments are not limited to the bottom emission structure, and theorganic light emitting diode display may have a dual emission structureby omitting the reflective layer 290 and forming the common electrode280 from a transparent electrode material.

As described above, each pixel electrode 240 may correspond to one ofthe pixels; and adjacent pixel electrodes 240 may be spaced apart fromeach other. In the present embodiment, referring to FIG. 2, the pixelelectrode 240 may include a first pixel electrode 210 under the redpixel 260R, a second pixel electrode 220 under the green pixel 260G, anda third pixel electrode 230 under the blue pixel 260B. The pixelelectrodes 210, 220, and 230 corresponding to the respective pixels mayeach have a differential structure. For example, the first pixelelectrode 210, the second pixel electrode 220, and the third pixelelectrode 230 may have different thicknesses from each other. Herein,the thickness of a pixel electrode refers to a thickness in a stackingdirection of each layer, i.e., in a direction from a bottom of the pixelelectrode toward the organic emission layer 201 and the commonelectrode.

As described above, the thicknesses of the first pixel electrode 210,the second pixel electrode 220, and the third pixel electrode 230 may bedifferent from each other. Accordingly, differences in the lifespan ofthe pixels may be reduced without an additional buffer layer under theRGB pixels.

FIG. 3 illustrates an enlarged cross-sectional view of a pixel electrodeof the organic light emitting diode display of FIG. 2. Referring to FIG.3, a structure of the pixel electrode according to the presentembodiment will be described in detail.

Referring to FIG. 3, in the organic light emitting diode displayaccording to the present embodiment, the first pixel electrode 210, thesecond pixel electrode 220, and the third pixel electrode 230 may beformed on the display substrate 100 where, e.g., the driving thin filmtransistors 50, etc., are formed.

Each of the pixel electrodes 210, 220, and 230 may be formed by stackingan ITO (indium tin oxide) layer and a Ag layer. For example, the pixelelectrodes 210, 220, and 230 may respectively include triple-layeredfilms 214, 224, and 234 respectively including first ITO layers 211,221, and 231, Ag layers 212, 222, and 232, and second ITO layers 213,223, and 233. In the present embodiment, the first ITO layers 211, 221,and 231 and the second ITO layers 213, 223, and 233 may each have athickness of about 50 Å to about 500 Å. The Ag layers 212, 222, and 232may have a thickness of about 50 Å to about 500 Å. The multilayerstructure of ITO/Ag/ITO may help ensure that transparent electrodeshaving excellent conductivity are formed.

A first hydrophobic layer 245 may be formed on the triple-layered filmsof ITO/Ag/ITO. The first hydrophobic layer 245 may include a thin filmhaving a thickness of about 30 Å to about 50 Å. In an implementation,the hydrophobic layer 245 may be an organic oxide film that is aboutequal to or thicker than a monomolecular layer.

The first pixel electrode 210 and the second pixel electrode 220 mayfurther include third ITO layers 215 and 225, respectively. The thirdITO layers 215 and 225 may be formed on the hydrophobic layer 245; and asecond hydrophobic layer 246 may be formed on the third ITO layers 215and 225. In addition, the first pixel electrode 210 may further includea fourth ITO layer 216 on top of the second hydrophobic layer 246 on thethird ITO layer 215. The third ITO layer 215, 225 and the fourth ITOlayer 216 may each have a thickness of about 50 Å to about 500 Å. Thesecond hydrophobic layer 246 on the third ITO layers 215 and 225 may bea thin film having a thickness of about 30 Å to about 50 Å. In animplementation, the second hydrophobic layer 246 may be an organic oxidefilm that is about equal to or thicker than a monomolecular layer.

As described above, the first pixel electrode 210, the second pixelelectrode 220, and the third pixel electrode 230 may include thetriple-layered films 214, 224, and 234 of ITO/Ag/ITO; and thetriple-layered films 214, 224, and 234 may each further include adifferent number of ITO layers thereon, so the pixel electrodes 210,220, and 230 have different thicknesses from each other. For example,the first hydrophobic layer 245 and second hydrophobic layer 246, whichmay be thin films, may be formed on the triple-layered films 214, 224,and 234 and the third ITO layers 215 and 225, respectively. Thus, thethird ITO layers 215 and 225 and the fourth ITO layers 216 may beselectively stacked without inhibiting electrical connection between theITO layers. With this structure of the pixel electrodes 210, 220, and230, differences in the lifespan of the emission layer 260, i.e., theRGB pixels 260R, 260G, and 260B, on each of the pixel electrodes 210,220, and 230 may be reduced.

Hereinafter, a fabricating method of an organic light emitting diodedisplay according to an embodiment will be described.

To fabricate an organic light emitting diode display, first, a displaysubstrate 100 made of, e.g., glass or the like, may be prepared. Aswitching thin film transistor, a driving thin film transistor, acapacitor element, etc. may be formed by stacking and patterning, e.g.,various lines, electrodes, insulation layers, etc. (not illustrated), onthe display substrate 100. After that, an organic light emitting diodemay be formed by forming a pixel electrode so as to be electricallyconnected to the driving thin film transistor, and forming an organicemission layer and a common electrode on the pixel electrode. In thepresent embodiment, the pixel electrode may be formed of a transparentelectrode; and a reflective layer may be additionally formed on thecommon electrode to form a bottom emission structure. The commonelectrode may be formed of a transparent electrode and the reflectivelayer may be omitted to form a dual emission structure. The organiclight emitting diode including the pixel electrode, the organic emissionlayer, and the common electrode may be formed. Then, an encapsulator,e.g., an encapsulation substrate or a thin film encapsulation layer, maybe formed on the organic light emitting diode to seal and protect theorganic light emitting diode, thereby fabricating an organic lightemitting diode display.

In the present embodiment, each pixel electrode may have a differentthickness in order to reduce differences in the lifespan of RGB pixelsof each organic emission layer. For example, hydrophobic layers may beformed on the pixel electrodes in order to provide different thicknessesof the pixel electrodes.

FIGS. 4A to 4G illustrate stages in a fabricating process of a pixelelectrode of an organic light emitting diode display according to anembodiment. Referring to FIGS. 4A to 4G, a pixel electrode formationprocess of the fabricating method of the organic light emitting diodedisplay, i.e., a process of forming a hydrophobic layer on a pixelelectrode and varying the thicknesses of each pixel electrode, will bedescribed in detail.

Referring to FIG. 4A, ITO layers 211′, 221′, and 231′, Ag layers 212,222, and 232, and ITO layers 213′, 223′, and 233′ may be sequentiallystacked and patterned on the display substrate 100 where, e.g., thedriving thin film transistor, etc. (not illustrated), are formed. Thelayers may be formed using the same mask, and accordingly, thetriple-layered films 214, 224, and 234 of ITO/Ag/ITO may be spaced apartfrom each other. Each of the ITO layers 211′, 221′, 231′, 213′, 223′,and 233′ may include amorphous ITO.

Referring to FIG. 4B, after the triple-layered films 214, 224, and 234of ITO/Ag/ITO are formed, a heat treatment may be performed. The heattreatment may be performed for about 30 minutes at a temperature higherthan about 150° C. By this heat treatment, the amorphous ITO of the ITOlayers 211′, 221′, 231′, 213′, 223′, and 233′ may be transformed intopolycrystalline ITO, thus forming first ITO layers 211, 221, and 231 andsecond ITO layers 213, 223, and 233.

Referring to FIG. 4C, after the first ITO layers 211, 221, and 231 andthe second ITO layers 213, 223, and 233 are formed by heat treatment, afirst hydrophobic layer 245 may be formed on each of the tripe layers214, 224, and 234. In the present embodiment, the first hydrophobiclayer 245 may be an organic oxide film that is naturally stacked andformed on the triple-layered films 214, 224, and 234 by, e.g., exposingthe thermally-treated triple-layered films 214, 224, and 234 to theambient environment.

In the course of the process, the organic oxide film may be stacked andformed in the ambient environment. This organic oxide film may be formedas a monomolecular layer or a thin film that is thicker than amonomolecular layer, and may include a hydrophobic material that doesnot dissolve well in water. Thus, the organic oxide film may not beremoved by washing during the fabricating process. For example, in thepresent embodiment, the naturally stacked and formed organic oxide filmmay be used as the first hydrophobic layer 245 without this washingprocedure, so that the pixel electrodes 210, 220, and 230 may have adifferential structure as will be described below. The naturally stackedand formed organic oxide film, e.g., the first hydrophobic layer 245,may be formed as a thin film having a thickness of about 30 Å to about50 Å, so that electrical connection between ITO layers is not blocked bythe first hydrophobic layer 245.

While the present embodiment refers to a case in which the firsthydrophobic layer 245 is naturally stacked and formed by the ambientenvironment, the first hydrophobic layer 245 may be artificially formed.Even when the first hydrophobic layer 245 is artificially formed, it maybe formed of a thin film to prevent electrical connection from beingbroken.

Referring to FIG. 4D, after the first hydrophobic layer 245 is formed,ITO layers 215′, 225′, and 235′ may be respectively formed on thetriple-layered films 214, 224, and 234. The ITO layers 215′, 225′, and235′ may include amorphous ITO, and may be formed using the mask used toform the triple-layered films 214, 224, and 234.

Referring to FIG. 4E, part of the ITO layer 235′ may be removed byetching. For example, a photoresist layer (not illustrated) may beformed on the ITO layers 215′ and 225′; and then the ITO layer 235′where the photoresist layer is not formed may be selectively removed byusing an etchant for selectively etching amorphous ITO. Then, thephotoresist layer may be removed. The ITO layers 215′ and 225′ under thephotoresist layer may not be etched because the etchant may not contactthem. The second ITO layer 233 of the triple-layered films 234 may bemade of polycrystalline ITO by heat treatment. Thus, the second ITOlayer 233 may not be etched by the etchant for selectively removingamorphous ITO. The first hydrophobic layer 245 may suppresspolycrystallization of the amorphous ITO of the ITO layer 235′ by thesecond ITO layer 233 formed of polycrystalline ITO and may facilitateselective etching.

Referring to FIG. 4F, after the part of the ITO layer 235′ includingamorphous ITO is removed, a heat treatment may be performed. The heattreatment may be performed for about 30 minutes at a temperature higherthan about 150° C. By this heat treatment, the amorphous ITO of the ITOlayers 215′ and 225′ may be transformed into polycrystalline ITO, thusforming third ITO layers 215 and 225.

After the heat treatment, a second hydrophobic layer 246 may be formedon the third ITO layers 215 and 225 and the triple-layered film 234. Thesecond hydrophobic layer 246 may be an organic oxide film that isnaturally stacked and formed by exposure to the ambient environment.Alternatively, the second hydrophobic layer 246 may be artificiallyformed. The second hydrophobic layer 245 may be formed as a thin filmhaving a thickness of about 30 Å to about 50 Å to prevent electricalconnection from being broken by the second hydrophobic layer 246.

Referring to FIG. 4G, an ITO layer including amorphous ITO may be formedon the second hydrophobic layer 246 by using the same mask as describedabove. Another selective etching process, similar to that illustrated inFIG. 4E, may be performed, thus forming a fourth ITO layer 216. Forexample, a photoresist layer (not illustrated) may be formed only on theITO layer corresponding to the first pixel electrode 210, among the ITOlayers including amorphous ITO formed on the triple-layered films 214,224, 234. Then, the ITO layers where the photoresist layer is not formedmay be selectively removed by using an etchant for selectively etchingamorphous ITO. Afterwards, the photoresist layer may be removed and thefourth ITO layer 216 may be formed.

Accordingly, the first pixel electrode 210 may include the third ITOlayer 215 and the fourth ITO layer 216 on the triple-layered film 214,the second pixel electrode 220 may include the third ITO layer 225 onthe triple-layered film 224, and the third pixel electrode 230 mayinclude the triple-layered film 234, thereby making the thicknesses ofthe pixel electrodes different from each other.

It is possible to provide a differential structure in which thicknessesof the pixel electrodes 210, 220, and 230 are varied by a heat treatmentprocess for polycrystallization of ITO and an etching process forselective etching. By this process, a number of steps of a depositionprocess using a mask may be decreased, occurrence of defects during thedeposition process may be reduced, and production yield may be improved.Moreover, productivity may be improved and manufacturing costs of theorganic light emitting diode display may be reduced.

According to the embodiments an additional buffer layer may beunnecessary and the deposition process using an additional mask may thusbe unnecessary. Accordingly, manufacturing costs of the organic lightemitting diode display may be reduced due to the decrease in the numberof deposition masks, defects during the deposition process may bereduced, and production yield may be increased.

The embodiments provide an organic light emitting diode display withreduced occurrence of defects during formation of a pixel electrode ofan organic light emitting diode having a differential structure.

The embodiments provide a fabricating method of an organic lightemitting diode display, which reduces manufacturing costs and improvesproductivity by reducing a number of steps of a mask deposition process.

Exemplary embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation.Accordingly, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made without departingfrom the spirit and scope of the present invention as set forth in thefollowing claims.

1. An organic light emitting diode display, comprising: a substrate; athin film transistor on the substrate; and an organic light emittingdiode on the substrate, the organic light emitting diode including apixel electrode, an organic emission layer, and a common electrode,wherein: the organic emission layer includes a red (R) pixel, a green(G) pixel, and a blue (B) pixel, the pixel electrode includes a firstpixel electrode, a second pixel electrode, and a third pixel electrodethat respectively correspond to the red pixel, the green pixel, and theblue pixel, the first pixel electrode, the second pixel electrode, andthe third pixel electrode each have different thicknesses, and the firstpixel electrode, the second pixel electrode, and the third pixelelectrode each include a first hydrophobic layer.
 2. The organic lightemitting diode display as claimed in claim 1, wherein: a thickness ofthe first pixel electrode is greater than a thickness of the secondpixel electrode, and a thickness of the second pixel electrode isgreater than a thickness of the third pixel electrode.
 3. The organiclight emitting diode display as claimed in claim 1, wherein: the firstpixel electrode includes a sequentially stacked first ITO (indium tinoxide) layer, Ag (silver) layer, second ITO layer, third ITO layer, andfourth ITO layer, the first hydrophobic layer is between the second ITOlayer and the third ITO layer, and the first pixel electrode furtherincludes a second hydrophobic layer, the second hydrophobic layer beingbetween the third ITO layer and the fourth ITO layer.
 4. The organiclight emitting diode display as claimed in claim 3, wherein the firstITO layer, the second ITO layer, and the third ITO layer each includepolycrystalline ITO.
 5. The organic light emitting diode display asclaimed in claim 1, wherein: the second pixel electrode includes asequentially stacked first ITO layer, Ag layer, second ITO layer, andthird ITO layer, and the first hydrophobic layer is between the secondITO layer and the third ITO layer.
 6. The organic light emitting diodedisplay as claimed in claim 5, wherein the second pixel electrodefurther includes a second hydrophobic layer, the second hydrophobiclayer being on the third ITO layer.
 7. The organic light emitting diodedisplay as claimed in claim 5, wherein the first ITO layer, the secondITO layer, and the third ITO layer each include polycrystalline ITO. 8.The organic light emitting diode display as claimed in claim 1, wherein:the third pixel electrode includes a sequentially stacked first ITOlayer, Ag layer, and second ITO layer, and the first hydrophobic layeris on the second ITO layer.
 9. The organic light emitting diode displayas claimed in claim 8, wherein the first ITO layer and the second ITOlayer each include polycrystalline ITO.
 10. The organic light emittingdiode display as claimed in claim 1, wherein the first hydrophobic layerhas a thickness of about 30 Å to about 50 Å.
 11. The organic lightemitting diode display as claimed in claim 1, wherein the organicemission layer further includes at least one of a hole injection layer,a hole transporting layer, an electron transporting layer, and anelectron injection layer.
 12. The organic light emitting diode displayas claimed in claim 1, further comprising a reflective layer on thecommon electrode.
 13. A fabricating method of an organic light emittingdiode display, the method comprising: providing a substrate; forming athin film transistor on the substrate; forming a pixel electrode on thethin film transistor; forming an organic emission layer on the pixelelectrode; and forming a common electrode on the organic emission layer,wherein: the pixel electrode includes a first hydrophobic layer and asecond hydrophobic layer, and thicknesses of portions of the pixelelectrode corresponding to a red pixel, a green pixel, and a blue pixelof the organic emission layer, respectively, are different from eachother.
 14. The method as claimed in claim 13, wherein: forming the pixelelectrode includes forming a first pixel electrode, a second pixelelectrode, and a third pixel electrode under each of and correspondingto the red pixel, the green pixel, and the blue pixel, respectively, athickness of the first pixel electrode is greater than a thickness ofthe second pixel electrode, and a thickness of the second pixelelectrode is greater than a thickness of the third pixel electrode. 15.The method as claimed in claim 13, wherein forming the pixel electrodeincludes: sequentially stacking a first ITO layer, a Ag layer, and asecond ITO layer; forming the first hydrophobic layer on the second ITOlayer; forming a third ITO layer on the first hydrophobic layer;removing a part of the third ITO layer; forming the second hydrophobiclayer on the third ITO layer; forming a fourth ITO layer on the secondhydrophobic layer; and removing a part of the fourth ITO layer.
 16. Themethod as claimed in claim 15, wherein forming the pixel electrodefurther includes polycrystallizing the first ITO layer and the secondITO layer prior to forming the first hydrophobic layer.
 17. The methodas claimed in claim 16, wherein polycrystallizing the first ITO layerand the second ITO layer includes a heat treatment.
 18. The method asclaimed in claim 16, wherein removing the part of the third ITO layerincludes: forming a photoresist layer on portions of the third ITO layercorresponding to the red pixel and the green pixel; etching portions ofthe third ITO layer corresponding to the blue pixel; and removing thephotoresist layer.
 19. The method as claimed in claim 15, whereinforming the pixel electrode further includes polycrystallizing the thirdITO layer prior to forming the second hydrophobic layer.
 20. The methodas claimed in claim 19, wherein polycrystallizing the third ITO layerincludes a heat treatment.
 21. The method as claimed in claim 19,wherein removing the part of the fourth ITO layer includes: forming aphotoresist layer on a portion of the fourth ITO layer corresponding tothe red pixel; etching portions of the fourth ITO layer corresponding tothe green pixel and the blue pixel; and removing the photoresist layer.22. The method as claimed in claim 15, wherein the first hydrophobiclayer and the second hydrophobic layer each have a thickness of about 30Å to about 50 Å.